Single-copy entanglement detection

Abstract

One of the main challenges of quantum information is the reliable verification of quantum entanglement. The conventional detection schemes require repeated measurement on a large number of identically prepared systems. This is hard to achieve in practice when dealing with large-scale entangled quantum systems. In this letter we develop a novel method by formulating verification as a decision procedure, i.e. entanglement is seen as the ability of quantum system to answer certain "yes-no questions". We show that for a variety of large quantum states even a single copy suffices to detect entanglement with a high probability by using local measurements. For example, a single copy of a $16$-qubit $k$-producible state or one copy of $24$-qubit linear cluster state suffices to verify entanglement with more than $95\%$ confidence. Our method is applicable to many important classes of states, such as cluster states or ground states of local Hamiltonians in general.